1. Field of the Invention
The subject invention relates to apparatus of applying glaze granules to tiles while the tiles are at a high temperature.
1. Description of Related Art
Processes for tile-making are known which provide for depositing granular glaze onto the tiles during their baking by heat treatment, i.e., when the tiles are at a high temperature. A process of such kind forms the subject matter of U.S. patent application Ser. No. 07/099,479 which is a divisional application of U.S. patent application Ser. No. 06/816,751 (now abandoned) which is based on Italian patent application No. 19589 A/85, in the name of the present applicant.
The application of the granular glaze onto the hot tiles entails numerous technological, physical and chemical problems, since account has to be taken of the fact that, in this process, tile temperature is propitiously higher than the melting temperature of at least some of the components of the glaze.
A glaze dispenser facing the tiles is subject to heating as a result of the heat transferred to it by the hot tiles, either by irradiation or by convection.
It might be supposed that this difficulty could be overcome by distancing the glaze dispensing unit from the tile, thus reducing the heat transferred to it by the tile. However, applicant has found that the increased fall height of the granular glaze gives rise to serious disadvantages.
In particular, if the fall height is excessive, the glaze becomes selectively subject to the action of the rising air-streams which occur in the presence of the hot tiles located within an environment of lower temperature; the granules of smaller size are clearly more likely to be slowed down by such rising air-streams, which effect a separation between the granules of different size. In addition, when the larger sized granules fall from a greater height, they acquire excessive kinetic energy which causes them to bounce off the surface of the tiles: as a result also of the rising air-stream, the separation of the small-sized fractions during the fall can cause uneven application due to a not perfectly constant and uniform fall of the glaze granules.
Moreover, the fact that the granules falling too fast tend to bounce off the tiles causes unevenness of application on the surface of the tile, especially proximal to the edges, and to the leading edge in particular, it follows that all these factors make it necessary for the fall height of the granular glaze to be kept as small as possible.
The spontaneous heating of the dispenser placed in close proximity to the incandescent tiles is therefore unacceptable, since the nearer the temperature of the dispenser comes to that of the tiles the more the lowest-melting fraction of the glaze is caused to melt, with the result that the melted glaze agglomerates in the dispenser and, in practice, prevents a correct dispensing of the glaze.